New design: 12V push-pull tube amplifier

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I was fiddling with spacecharge tubes for a while and I'm very exited about them. Now I've finally found a suitable small OPT with CT primary (not made for tubes but should withstand this). So, I'm planning a pushpull guitar amp with 12V power transformer.

The problems are - of course - the PI and the power stage. The preamp is not a question, it already worked in SE design.

spacecharger_pp_preliminary.jpg


From my experience all the 12V tubes work (sound) better with grid-leak bias, that's why the output stage looks so stupid and I'm shure I'm missing something here.

Datasheetz::::

12AJ6 - hi-mu triode
12FM6 - medium-mu triode
12DU7 - output tetrode
 
I agree that a higher-output phase inverter is needed - I'd probably use a pair of 6GM8 dual triodes and a pair of 12K5s - since I have 'em. G1 is usually at 12V and G2 used as control grid - I wonder about that 12DU7 data sheet...

At 15V, some cathode bias may be necessary on the outputs - the 12K5 has a more complete data sheet, and says there is -2V bias (from rectified signal) with 2.2 meg grid resistor, and draws 40 mA with no signal.

Sounds like a fun project - I'd run it from a 12V gel-cell battery, of course!
 
Hello, engels...

Where go this condenser into PI and power tubes?.

What is PI or where go this condenser's?

I am spanish and not understand good the site of this condenser's

This is one interesting idea, i have some run amps whit single 12k5, and i see for one probe whit two spacecarge in phushpull for more power.

The power of this in phush pull is...? Aproximate?

Thanks.
 
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6922 also works quite well on 12 - 20v B+
I was testing my cct with 135v on it and tried a 9v for the b+ supply.
The gain was about half but the sound was still good.
at 46v B+, The + VAS stage rail, the output levels are identical to the 135v supply.
I did not do any distortion tests at the different B+ voltage levels
I would use a voltage doubler and RC filter for the 15v supply as current is very low.
you could then easily get 25v for the amplification stages
 
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PRR

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"Space Charge Tubes" work very differently.

Start with a several-grid tube.

Pull a "large" current from G1. Much more than you will take from Plate.

Put your *signal* in at grid 2.

The large current to G1 leaves a cloud of loose electrons around G1. Relatively lower plate voltages can attract these, easier than they could pull right from cathode. This plate current can be controlled by G2. G2 is typically negative of cathode and typically draws no grid current.

The drawback is a heavy drain on B+, and high G1 dissipation. However down around the 12V range, the worst G2 current is much less than heater current, which comes from the same battery (though needs less filtering against generator hash). G1 dissipation may not be too high; tubes sold for the purpose are made with tough G1.

The other drawback is that these often are "odd" or "poor" triodes or tetrodes, with excess curvature or/and kinks. Good enough to eliminate 250V vibrator supplies in 1950s car radio, not a real exacting application. (Power stage would be a 2N301 Ge transistor.)
 
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